Glozz hashcode mechanism

Could be useful when writing glozz XML files
Generalise glozz-dump to swiss-army-knife type
glozz hashcode utility
Span len argument
Preferences distinct from EDUs
Ability to filter nodes/rels on graph creation

Seems a bit too sensitive to annotation error to be practical though :-/
Colour non-EDUs red when graphing for STAC
visualisation: label nodes by order of their spans
Right frontier constraint checking